The human skeleton is the internal framework of the human body. It is composed of around 270 bones at birth–this total decreases to around 206 bones by adulthood after some bones fuse together. The bone mass in the skeleton reaches maximum density around age 21. The human skeleton can be divided into the axial skeleton and the appendicular skeleton. The skeleton serves six major functions: support, movement, protection, production of blood cells, storage of minerals, and endocrine regulation.